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Old 2nd April 2006, 09:09 PM   #21
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Quote:
Originally posted by titanchen68
Thanks a lot ....
So , if the clamp circuit put in the error-amp will get better than clamp in the pre-amp , right ???
You said it will not getting an accurate clamp by using zener, but it seems to be a good ideal for now.

I still do not understand the different between the clamping around the error-amp and in the pre-amp.
Isn't it to clamp the input signal not exceed the triangle wave amplitued ??

what do you feel that i clamp the input signal amplitude to be 75% of triangle wave amplitude ??
Is it too lower or higher???
That is becoming my guess however I am now seeing problems elsewhere. For the moment it seems to be the easiest solution. For now, yes back to back zeners seem to be an easy fix but you should check the manufacturers data. I'm not certain but I think you will find that higher power devices, within reason, have better characteristics. They will have higher capacitance though.

If you clamp around the error amplifier then you gaurantee the level at which you clamp. If you clamp the input signal you have to take into account the effects of both the input signal and that from the feedback signal. I'm not saying it won't work but the behaviour is likely to be more complex.

As for the level you might choose then, assuming there is nothing else upsetting things then, unless you can calculate a true figure for deadtime in your circuit, it's not unreasonable to use the circuit itself to find out what the level should be.

DNA
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Old 4th April 2006, 05:53 AM   #22
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I have bought the 3v zener diode use to clamp in error-amp.
And I'll try it later.

Yesterday , i want test the highest output amplitude.
So , i use function generator be the input signal.
I am testing in No Load. ( It seems not a good ideal )
When the inpug signal too big to clip the output signal that after LC filter.
The outuput mosfet burned out immediatly.
Is that right ???

Because i want to test the relationship between input signal and output waveform.
do i have anyother way to test ???
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Old 4th April 2006, 10:14 AM   #23
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Do you want to say that when you clip your amp the output stage mosfet gets burned immidiately...

K a n w a r
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Old 4th April 2006, 11:36 AM   #24
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Quote:
Originally posted by Workhorse
Do you want to say that when you clip your amp the output stage mosfet gets burned immidiately...

K a n w a r
Yes , i am .
Is that strange ???
Because I don't why , i only think is ShotThrought !
But i remember the Ir2110 has internal Dead time , i think it will not happen.
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Old 4th April 2006, 08:14 PM   #25
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Quote:
Originally posted by titanchen68
I have bought the 3v zener diode use to clamp in error-amp.
And I'll try it later.

Yesterday , i want test the highest output amplitude.
So , i use function generator be the input signal.
I am testing in No Load. ( It seems not a good ideal )
When the inpug signal too big to clip the output signal that after LC filter.
The outuput mosfet burned out immediatly.
Is that right ???

Because i want to test the relationship between input signal and output waveform.
do i have anyother way to test ???

Quote:
Originally posted by titanchen68


Yes , i am .
Is that strange ???
Because I don't why , i only think is ShotThrought !
But i remember the Ir2110 has internal Dead time , i think it will not happen.
Sorry, I'm not sure I can help here.

Although some IRF drivers do include deadtime the IR2110 does not so you have to generate it in some other way. It looks like your gate diode/resistor combination is being used to achieve this and if things are not going wrong during normal operation the method may be working.

I'm sure someone else has mebtioned the bootstrap supply for the IC not being recharged during clipping. Your circuit shows a 40V supply but I assume that is a mistype. Maximum current drain is specified as 250uA so a 15V supply would drop to undervoltage lockout in about 18mS, which is quite a low frequency.

Even so you might expect the undervoltage lockout to prevent nasty things from happening although the data sheet makes no mention of drive or levels under these conditions.

Sorry, at the moment nothing else comes to mind...

DNA
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Old 5th April 2006, 03:13 AM   #26
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Hi Titan,

If the bootstrap is not sufficient to provide enough voltage to charge the gates of mosfet, then this could happen during clipping...yes i had experienced this...you can also increase the boot Cap value upto 50MFD to maintain sufficient charge in case of hard clipping....

Second best way is to use an isolated floating supply reference to the source of High side Mosfet and then feed the VB from it, I have used this technique to enable the gate driver to give as much as charge to the gates of mosfets with Qg>300nC...No destruction at hard clipping with this technique....

K a n w a r
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Old 5th April 2006, 11:25 AM   #27
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Thanks for replying....

I will try to increase the bootstrape cap to 50uF.
That sounds a good ideal , But in this technique , don't i still use large bootstrape cap to maintain the sufficient charging ???

After this project , i get a summy for voltage disigned.
The +/-RAIL voltage effected by :
1. maximum output power
2. triangle amplitude and output amplitude of error-amp

This project i want to create a 400Wrms in 4ohm
(didn't consider about voltage drop in mosfet)
so , i use a +/-55V rail voltage , 56*56/4/2 = 392Wrms
But i clamp my error-amp to 3.6v , the triangle wave amplitude is 4v.
In maximum , i only get 90% of maximum ouput voltage.
And only get 81% of maximum output power.
Only 392*0.81 = 317Wrms.

Did i get any wrong ???
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Old 6th April 2006, 03:14 AM   #28
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Have you used the 50MFD cap....whats the result after that?

K a n w a r
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Old 6th April 2006, 05:57 AM   #29
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Quote:
Originally posted by Workhorse
Have you used the 50MFD cap....whats the result after that?

K a n w a r
I add a DC protect , and used the 50uF bootstrape cap.
When the output wave amplitude near +/-RAIL, after about 1sec , the DC protect working.
But the output mosfet didn't burned.
I think if didn't have dc proctect , the mosfet will burned,too.
But i don't know what will happen if i didn't add the dc protec circuit.
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Old 6th April 2006, 11:13 AM   #30
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Remove your DC protection and then check the clipping action....
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